A surgical microscope of the kind described above is known from U.S. Pat. No. 5,126,877. This surgical microscope comprises an illuminating arrangement wherein illuminating light is made available via the exit end of a light conductor perpendicularly to the optical axis of the microscope main objective. This illuminating light having a beam path, which is parallel to the optical axis of the microscope main objective, is deflected to the microscope main objective via a first deflecting element and a second deflecting element on the side of the microscope main objective facing away from the object region. The illuminating light is guided with a first beam path through the microscope main objective to the object region and with a second beam path. The first beam path runs axis-near to the optical axes of the viewing beam paths of the microscope and the second beam path illuminates the object region with inclined light and has an axis-far course with reference to the optical axes of the viewing beam paths of the surgical microscope. The illuminating field corresponds to the image of an illuminating field diaphragm in the object region with the diaphragm being arranged at the exit end of the light conductor and the image of the illuminating field diaphragm being generated by means of the illuminating optic.
With the use of surgical microscopes in surgical procedures, different requirements are placed on the illumination of the area of surgery depending upon the medical specialty. In surgical procedures in ENT surgery and neurosurgery, the area of surgery is illuminated with axis-near inclined illumination with reference to the viewing beam paths so that especially narrow, deep body cavities can be illuminated without the formation of shadows. For microsurgical procedures on the eye, illuminating light reflected diffusely from the retina is used which appears to a surgeon examining the lens of the patient eye as red transmitted light in order to make visible transparent structures in the anterior region of the patient eye.
In ophthalmologic surgical procedures, it is advantageous when a surgeon has the possibility in a surgical microscope to illuminate the area of surgery with illuminating light at different angles with reference to the optical axes of the viewing beam paths in order to be able to adjust the contrast of the viewed image in this manner.
United States published patent application US 2005/0128574 A1 describes an illuminating arrangement for an ophthalmologic surgical microscope which has an illuminating beam path which effects an image of the illuminating pupil of the illuminating arrangement on the retina of a patient eye under examination.
United States published patent application US 2007/0263173 A1 discloses a surgical microscope having an illuminating arrangement wherein a beam splitter element is provided in the stereoscopic viewing beam paths in order to coaxially superpose illuminating light onto the viewing beam paths with this illuminating light being directed to the object region through the microscope main objective.
International patent application having publication number WO 2007/110207 discloses a surgical microscope having an illuminating arrangement which provides illuminating light with an illuminating beam path which is guided through the microscope main objective to the object region. The illuminating arrangement includes a Köhler illuminating optic. A reflex diaphragm is mounted in the illuminating beam path. The reflex diaphragm effects a shading of such illuminating light which would get into the viewing beam paths of the surgical microscope because of reflections on the microscope main objective. In this way, disturbing reflections in the viewed image of the surgical microscope can be avoided.
U.S. Pat. No. 4,715,704 discloses an ophthalmologic surgical microscope having an illuminating arrangement which includes a retina protective diaphragm pivotable into and out of the illuminating beam path. The retina protective diaphragm is configured as an annularly-shaped diaphragm. In the pivoted-in state, the annularly-shaped diaphragm is disposed in a plane conjugated to the object plane of the surgical microscope and blocks illuminating light or attenuates such illuminating light which could otherwise reach the retina through the iris of a patient eye.
U.S. Pat. No. 6,011,647 discloses a surgical microscope which comprises an illuminating arrangement which makes possible to illuminate the object region in different configurations for the illuminating light. The illuminating arrangement can, on the one hand, make available illuminating light via an illuminating field diaphragm which is imaged into the object region via the microscope main objective. On the other hand, the illuminating arrangement can illuminate the object region with illuminating light in a configuration wherein the coiled filaments of a lamp or the exit end of a light conductor are imaged into the object region through the microscope main objective.
German utility model registration 20 2004 019 849 U1 discloses a surgical microscope which makes possible the illumination of an object region with differently configured illuminating light through the microscope main objective. In a first configuration for illuminating light, an illuminating field diaphragm is imaged into the object region via the microscope main objective corresponding to U.S. Pat. No. 6,011,647. Corresponding to the second configuration, the illuminating light passes through a diffuser which is arranged at a light source imaged into the object region.